Milk lymphocyte profile and macrophage functions: new insights into the immunity of the mammary gland in quarters infected with Corynebacterium bovis

Vitória M Silva,Carla M Ordinola-Ramirez,Alice M M P Della Libera,Camila F Batista,Marina T Souza,Eduardo M R Sanchez,Fernando N Souza,Alexandre J Alves,Artur C C Fernandes,Maiara G Blagitz,Luciana Da Costa

doi:10.1186/s12917-021-02989-5

Abstract

BackgroundsThe present study explored the viability of bovine milk macrophages, their intracellular production of reactive oxygen and nitrogen species (RONS), and their phagocytosis of Staphylococcus aureus, as well as the profile of lymphocytes, from healthy udder quarters and udder quarters infected by Corynebacterium bovis. The study included 28 healthy udder quarters from 12 dairy cows and 20 udder quarters infected by C. bovis from 10 dairy cows. The percentages of macrophages and lymphocytes were identified by flow cytometry using monoclonal antibodies. Macrophage viability, RONS production, and S. aureus phagocytosis were evaluated by flow cytometry.ResultsMilk samples from quarters infected with C. bovis showed a lower percentage of macrophages but an increased number of milk macrophages per mL and a higher percentage of macrophages that produced intracellular RONS and phagocytosed S. aureus. No effect of C. bovis infection on macrophage viability was found. Udder quarters infected by C. bovis showed a higher percentage of T cells and CD4+ T lymphocytes, but no effect was found on the percentage of CD8+ CD4− T, CD8− CD4− T, or B lymphocytes.ConclusionsThus, our results corroborate, at least in part, the finding that intramammary infections by C. bovis may offer protection against intramammary infections by major pathogens.

Highlights

Corynebacterium bovis is one of the bacteria most commonly isolated from aseptically collected bovine milk samples worldwide that are subjected to microbiological examination to identify the pathogens that cause bovine mastitis [1,2,3,4]
Milk samples from quarters infected with C. bovis showed a lower percentage of macrophages but an increased number of milk macrophages per mL and a higher percentage of macrophages that produced intracellular reactive oxygen and nitrogen species (RONS) and phagocytosed S. aureus
Udder quarters infected by C. bovis showed a higher percentage of T cells and CD4+ T lymphocytes, but no effect was found on the percentage of CD8+ CD4− T, CD8− CD4− T, or B lymphocytes

Summary

Introduction

Corynebacterium bovis is one of the bacteria most commonly isolated from aseptically collected bovine milk samples worldwide that are subjected to microbiological examination to identify the pathogens that cause bovine mastitis [1,2,3,4]. Despite its high prevalence in the etiology of intramammary infections in cattle, C. bovis is considered a minor mastitis pathogen with limited clinical significance [5]. From another point of view, it has been considered part of the udder core microbiota with potential protective role against dysbiosis [6,7,8]. This bacterium colonizes the teat apices [9, 10], teat canal [11] but can be isolated from the teat cistern, gland cistern, and mammary parenchyma [12]. No effect on milk production [4, 14] or on the percentage of fat, protein, casein, and total solids was described [4]

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